AB0965 Serial serology testing in patients with psoriatic arthritis- Should it be done?
Authors: S. Sundanum, D. Veale, C. Orr, L. O’neill, F. Young
Journal: Annals of the Rheumatic Diseases (2022)

Background The diagnosis of psoriatic arthritis (PsA) is largely based on clinical phenotype due to the heterogeneity of the presenting features, which can include synovio-entheseal disease, dactylitis, skin and nail disease, uveitis and axial involvement. (1) In contrast to rheumatoid arthritis (RA), PsA is a seronegative inflammatory arthropathy. Rheumatoid factor (RF) and Anti-CCP antibodies are usually absent in PsA, and if patients do have positive serological findings for RF or CCP, the titres tend to be low. (2) Seronegativity for RF has a significantly high discriminant value in the Classification Criteria for Psoriatic arthritis (CASPAR), such that a negative RF forms one of the five possible criteria; thus serological testing is often done once at the initial diagnostic appointment. (3) A previous study in the context of RA has shown that there is a tendency for repeated serological testing with as much as 70% of patients having RF tested more than once.(4) Repeated testing amounts to additional expense and is rarely needed in PsA. The literature on the frequency of repeated serology testing in PsA patients is absent. Objectives To determine how often was serology for RF and anti-CCP antibodies repeated in a PsA cohort. Methods A cohort of consecutive patients attending the rheumatology clinic at our centre with a diagnosis of PsA were included. We reviewed the laboratory results of individual patients to determine how many times each patient had been tested for RF and anti-CCP antibodies. Results 118 patients with a diagnosis of PsA were included. 117 patients had RF antibody testing at least once and all 118 patients had a minimum of one anti-CCP antibody test. 59/117 (50.4%) patients had RF checked more than once and 28/117 (23.9%) had testing at least 3 times. 3 patients had an initial positive RF which was negative on subsequent testing. Anti-CCP antibody was checked on all 118 patients. 41/118 (34.7%) patients had anti-CCP checked more than once and 13/118 (11.0%) patients had testing at least 2 times. One patient had an initial equivocal anti-CCP antibody titre which was subsequently negative on repeat testing. Conclusion As opposed to RA, PsA has not been associated with the presence of circulating antibodies. The presence or absence of RF in PsA patients has for long been a subject of debate. (3) In cases of peripheral polyarticular PsA, which may be difficult to distinguish from RA, serological testing can be useful to identify RA. However, studies have found that RF can be present in 5-13% of PsA patients. (5) In the context of RA, serological conversion from negative to positive is infrequent and repeat testing is not recommended. (6) Over half of the patients in our PsA cohort had repeated RF testing. Certainly this is unlikely to be helpful or cost effective and serial serology measurements in PsA patients should be avoided. References [1]Veale DJ, Fearon U. The pathogenesis of psoriatic arthritis. The Lancet. 2018;391(10136):2273-84. [2]Merola JF, Espinoza LR, Fleischmann R. Distinguishing rheumatoid arthritis from psoriatic arthritis. RMD Open. 2018;4(2):e000656. [3]Veale DJ, Fearon U. What makes psoriatic and rheumatoid arthritis so different? RMD Open. 2015;1(1):e000025-e. [4]Orr C, Young F, Veale DJ. AB0243 How Often Are Serology Tests Repeated in RA Patients, and What Are the Merits? Annals of the Rheumatic Diseases. 2015;74(Suppl 2):972. [5]Punzi L, Podswiadek M, Oliviero F, Lonigro A, Modesti V, Ramonda R, et al. Laboratory findings in psoriatic arthritis. Reumatismo. 2007;59 Suppl 1:52-5. [6]Reid AB, Wiese M, McWilliams L, Metcalf R, Hall C, Lee A, et al. Repeat serological testing for anti-citrullinated peptide antibody after commencement of therapy is not helpful in patients with seronegative rheumatoid arthritis. Internal Medicine Journal. 2020;50(7):818-22. Disclosure of Interests None declared